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Spanish boffins unwrap anti-magnetic cloak

How to hide a magnet

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No, I don’t mean “non-magnetic”: if you wrap a magnet in cotton, you can still detect the magnet outside. “Anti-magnetic” means you can put a magnet inside and not detect it from the outside, and similarly, from the inside, you can’t detect outside magnetic fields.

That is what a group of scientists working in Spain claim they have designed. The role of such a material could be, for example, to allow patients with magnetically-sensitive devices (like a cochlear implant or pacemaker) to undergo procedures that depend on magnetic fields (like MRI). It would also be useful in defending ship hulls against magnetically-operating mines.

At the moment, it’s only a design, but the group from Universitat Autònoma de Barcelona believes that by starting with an inner superconducting layer, overlaid by ten layers of metamaterials, the design can be built.

As the paper claims: “our device is feasible and needs only two kinds of available materials: superconductors and isotropic magnetic materials.”

The latter describes materials whose magnetic properties are directionally-dependent. These are required, the authors say, because otherwise the superconducting cloak would distort outside magnetic fields (and therefore be detectable).

If my reading of the paper is accurate, it would be simpler to just overlay superconductors for all layers, but it’s easier in the real world to reduce the number of superconductors used. The temperature behavior of the superconductor is important in the design, since the magnetic behavior of the superconductor changes with temperature – also possibly allowing the cloak to be switched on or off according to its temperature.

While the authors’ design envisages a cylinder concealing a single small magnet, they also believe other shapes are feasible – and that one day, anti-magnets could be practical enough to conceal metals from instruments like airport scanners. The paper was authored by Alvaro Sanchez, Carles Navau, Jordi Prat-Camps, and Du-Xing Chen, and is published today in the New Journal of Physics. ®

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